Recent years have seen a global increase in asthma prevalence. This has coincided with modifications to the home environment resulting in changes to the indoor air quality. This article considers the links between indoor pollution and asthma. Exposure to a range of substances is examined. Airborne allergens such as those from house dust mites may be important. Pollution from particulate materials associated with combustion and smoking is discussed, as is the role of chemical vapors and gases including nitrogen dioxide, sulfur dioxide, and volatile organic compounds. The efficacy of various environmental controls to limit the impact of these pollutants is explored.